The present invention relates to novel crystals of a vitamin D derivative and, more specifically, to novel crystals of a vitamin D derivative which are obtained by purifying the vitamin D derivative through a reverse phase chromatography and then crystallizing the purified derivative from an organic solvent. The present invention also relates to a method for purifying a vitamin D derivative which comprises a crystallization step.
A variety of vitamin D derivatives are known to have useful physiological activities. For example, JP 6-23185 B/1994 discloses that a 1xcex1-hydroxyvitamin D3 derivative represented by the following general formula: 
wherein R1 denotes an amino group or the formula ORxe2x80x2 where Rxe2x80x2 denotes a lower alkyl group having 1 to 7 carbon atoms which is unsubstituted or substituted by a hydroxyl group, a halogen atom, a cyano group or an acylamino group, and R2 denotes a hydrogen atom or a hydroxyl group, is useful as a therapeutic agent for diseases caused by calcium dysbolism or as an anti-tumor agent.
1xcex1,25-dihydroxy-2xcex2-(3-hydroxypropoxy)vitamin D3 (also called as ED-71) which is one of the compounds covered by the above general formula is an active form of a vitamin D derivative having a bone forming action and thus is in a way to be developed as a therapeutic agent for osteoporosis.
Once such a vitamin D derivative is established as a therapeutic agent, it should be highly purified and be supplied in bulk and steadily. Therefore, it is desired to establish a method for manufacturing a vitamin D derivative as soon as possible.
In particular, ED-71 has been obtained only in an amorphous form and there is no reported isolation of ED-71 in a crystalline form.
An object of the present invention is to establish a method for preparing a highly purified vitamin D derivative, especially ED-71, which makes it possible to supply the product in bulk and steadily.
Another object of this invention is to provide crystals of a vitamin D derivative which may be obtained by purifying a crude or preliminarily purified product of the vitamin D derivative.
Another object of this invention is to provide a method for purifying a vitamin D derivative which comprises a crystallization step.
A further object of this invention is to provide a method for purifying the pre form compound of ED-71, which comprises a crystallization step, and to provide a purified pre form compound obtained by the method.
A still further object of this invention is to provide novel compounds which are secondarily formed during the synthesis and purification of a vitamin D derivative.
We have conducted extensive research on the following points which are issued during the synthesis and purification of ED-71 from its provitamin D derivative (pro form): (1) the effect of impurities in the pro form on the HPLC preparative purification of ED-71; (2) the stability of ED-71 and its previtamin D derivative (pre form) to heat, light and oxygen; (3) the handling of ED-71 which exhibits a high physiological action even in a extremely small dose; and (4) the possibility of the purification of ED-71 by crystallization. As a result of the research, we have found that crystals of ED-71 can be obtained in gram order by recrystallizing the pro form from methanol, subjecting the recrystallized pro form to a photo-reaction at a low temperature and then a thermal isomerization reaction, purifying the isomerized product by a reverse phase HPLC, concentrating the eluate, and then crystallizing the residue from ethyl acetate, and have completed the present invention. Further, we have determined the structure of by-products which are originally contained in the pro form or formed during the photo-reaction and found that some compounds of them are novel.
According to one aspect of the present invention, crystals of the compound represented by formula (I): 
are provided.
According to another aspect of the present invention, crystals of a vitamin D derivative which are obtained by purifying a crude or preliminarily purified product of the vitamin D derivative through a reverse phase chromatography and then crystallizing the purified derivative from an organic solvent, are provided.
According to a further aspect of the present invention, a method for purifying a vitamin D derivative which comprises subjecting the vitamin D derivative to a reverse phase chromatography is provided.
According to a further aspect of the present invention, a method for purifying a vitamin D derivative which comprises crystallizing the vitamin D derivative from an organic solvent is provided.
According to a further aspect of the present invention, a method for purifying a vitamin D derivative which comprises purifying a crude or preliminarily purified product of the vitamin D derivative through a reverse phase chromatography and then crystallizing the purified derivative from an organic solvent is provided.
According to a further aspect of the present invention, a method for purifying the compound represented by formula (II): 
which comprises recrystallizing a crude or preliminarily purified product of the compound represented by formula (II) from an alcohol is provided.
According to a further aspect of the present invention, a purified product of the compound represented by formula (II): 
which is obtained by recrystallizing a crude or preliminarily purified product of the compound represented by formula (II) from an alcohol is provided.
According to a further aspect of the present invention, a method for preparing a purified product of the vitamin D derivative represented by formula (I): 
which comprises recrystallizing a crude or preliminarily purified product of the compound represented by formula (II): 
from an alcohol, subjecting the recrystallized compound of formula (II) to an ultraviolet light radiation and then a thermal isomerization reaction to give a vitamin D derivative represented by formula (I), purifying the crude or preliminarily purified vitamin D derivative of formula (I) through a reverse phase chromatography, and crystallizing the vitamin D derivative of formula (I) from an organic solvent, is provided.
According to a still further aspect of the present invention, the compound represented by formula (III): 
and the compound represented by formula (IV): 
are provided. These compounds are contained in the reaction mixture obtained by the ultraviolet light radiation and the subsequent thermal isomerization reaction of the pro form of ED-71.